One of the goals of multiferroic research is the development of new devices that take advantage of the coupling between magnetization and electric polarization. For instance in magnetoelectric (ME) memory devices the magnetic bits can be controlled by electric fields without the need to apply electric currents. We demonstrate the optical readout of ME memory states in the antiferromagnetic (AFM) and antiferroelectric (AFE) LiCoPO4, based on the strong absorption difference of THz radiation between its two types of ME domains. This unusual contrast is attributed to the dynamic ME effect of the spin-wave excitations, as confirmed by our microscopic model. Our proof-of-principle study demonstrates the control and the optical readout of ME domains in LiCoPO4 and layes the foundation for future ME devices based on AFE-AFM insulators.

*This work was supported by the Hungarian Research Funds OTKA K 108918, OTKA PD 111756, National Research, Development and Innovation Office NKFIH, ANN 122879 and Bolyai 00565/14/11, by the Deutsche Forschungsgemeinschaft via theTransregional Research Collaboration TRR 80, and by the Estonian Ministry of